1. Field of the Invention
The present invention relates to the field of variable gain amplifiers and the control thereof.
2. Prior Art
Many applications require a variable gain amplifier with a gain versus control voltage characteristic that is log-linear. Such control characteristic, often also referred to by other names, may be characterized by a gain control characteristic wherein the output of the gain controlled amplifier in db is a substantially linear function of the gain control voltage, preferably over as much of the gain control range of the amplifier as possible.
One prior art gain control method includes a control loop that is difficult to stabilize. A simpler prior art variable gain amplifier is a transconducter loaded with a pair of devices operated as a current steering mechanism, but generating a log-linear characteristic with this variable gain amplifier has not been demonstrated. By way of example, U.S. Pat. No. 5,572,166 discloses a Linear-In-Decibel Variable Gain Amplifier for an RF signal variable gain amplifier, though the technique disclosed therein is not applicable to current steered variable gain amplifiers.